Characterising the role of the Amyloid Precursor Protein and Glucagon-like peptide-1 analogues in Age-Related Macular Degeneration

Sultan, Fatima and Parkin, Edward (2022) Characterising the role of the Amyloid Precursor Protein and Glucagon-like peptide-1 analogues in Age-Related Macular Degeneration. Masters thesis, Lancaster University.

Text (2022FatimaSultanMSc(by research))
2022FatimaSultanMSc_by_research_.pdf - Published Version
Download (5MB)

Abstract

Age-related macular degeneration (AMD) is a progressive retinal neurodegenerative disorder characterised, in some forms of the disease, by the loss of photoreceptors and the underlying retinal pigment epithelium (RPE) in the macula due to the accumulation of extracellular deposits known as “drusen”. A major component of drusen deposits is the Alzheimer’s disease (AD)-related amyloid beta (Aβ)-peptide, a 4kDa peptide derived from the larger amyloid precursor protein (APP) through sequential cleavage by enzymes known as β- and γ-secretases. Alternatively, in the ‘non-amyloidogenic’ pathway, APP can be processed by a third enzyme, α-secretase, which cleaves within the Aβ region of the protein thereby preventing the production of toxic peptides as well as producing a larger soluble fragment, sAPPα, known for its neuroprotective and neurotrophic properties. The current project aims to characterise the role played by APP and its proteolytic fragments in AMD using human retinal pigment epithelial cells (ARPE-19) and UV-A light (a known AMD risk factor) as the stressor. In addition, a group of diabetes drugs known as Glucagon Like Peptide-1 (GLP-1) analogues that have previously been purported to reduce neuronal death in AD and Parkinson’s Disease (PD) have been tested for their ability to protect ARPE-19 cells against stress-inducing reagents relative to AMD (UV-A light, hydrogen peroxide and Aβ-peptides). The results of the current study demonstrate that endogenous cell-associated full-length APP expression was depleted in ARPE-19 cells following UV-A irradiation. Furthermore, β-secretase but not α-secretase processing of the protein was reduced. Small interfering RNA-mediated depletion of endogenous APP or γ-secretase (but not α- or β-secretase) inhibition ablated the detrimental effect of UV-A on cell viability. In contrast, α-secretase and, possibly, γ-secretase but not β-secretase activity appeared to promote the longer-term proliferation of ARPE-19 cells in the absence of UV-A irradiation. Furthermore, two of the GLP-1 analogues tested, liraglutide and lixisenatide, were able to restore cell viability after UV-A exposure. Collectively, these data indicate clear links between the expression/proteolysis of APP and the proliferation and resistance of ARPE-19 cells to UV-A irradiation. Whilst these effects are clearly differential, the data warrant further investigation of the role played by APP in AMD. Furthermore, the protective effects against UV-A shown by liraglutide and lixisenatide warrant further investigation of the molecular mechanisms involved with a view to identifying new drug targets for the prevention or treatment of retinal neurodegenerative diseases such as AMD.